1. Field of the Invention
The present invention relates to thermite reactions in electrolytic cells. More particularly, the present invention relates to systems and methods for the detection and/or prevention of thermite reactions in electrolytic cells.
2. Description of the Related Art
Electrolysis of alumina within an electrolytic cell is the major industrial process for the production of aluminum metal. In an aluminum electrolytic cell, an electrical current is passed between an anode and a cathode immersed within a bath of molten cryolite containing dissolved alumina. The electrical current causes the deposition of aluminum metal on the cathode. Commonly, the anodes are made of carbon or graphite materials. Carbon anodes are consumed during the aluminum production process, producing carbon dioxide, and must be replaced frequently.
In some electrolytic cells, the use of substantially “non-consumable” or “inert” anodes offer a cost effective and more environmentally sound alternative to carbon anodes.
However, when the inert anode includes metal oxides, there is a possibility of a thermite reaction between the metal oxides and the aluminum metal in the electrolysis cell, leading to possible cell failure or cell eruption.
Thermite reactions are highly exothermic oxidation-reduction reaction which occurs—between metal oxides and another metal, such as aluminum, in the presence of heat.
For example, typical thermite reactions that can occur in an electrolytic cell are set out below as Equations 1 and 2.MxOy (metal oxide)+2Y/3Al (metal)→XM+Y/3Al2O3+heat  (eq. 1)Fe2O3 (iron oxide)+2Al (aluminum metal)→2Fe+Al2O3+heat  (eq. 2)
As illustrated in Equation 2, because aluminum forms stronger bonds with oxygen than iron, aluminum metal reduces iron oxide to produce aluminum oxide, iron, and large amounts of heat.
As in other electrolytic metal production processes, the electrolytic production of aluminum involves high heat within an electrolytic cell (e.g. temperatures of up to 950° C.) and the presence of metal (aluminum) to fuel a thermite reaction. Thus, under certain operating conditions, using inert anodes having metal oxides may cause a thermite reaction within the electrolytic cell.